Different Types of SQL Server Functions

Estimated study time: 16 minutes. A clear breakdown of every function type in SQL Server.

SQL Server functions let you reuse logic inside queries instead of repeating the same calculation everywhere. Broadly, they fall into four categories: scalar, aggregate, window, and table-valued functions.

1. Scalar Functions

Return a single value based on the input. Built-in examples include UPPER(), LEN(), and GETDATE().

SELECT UPPER(first_name), LEN(first_name) FROM employees;

2. Aggregate Functions

Operate on a set of rows and return one summary value — SUM(), AVG(), COUNT(), MIN(), MAX().

SELECT department, AVG(salary) FROM employees GROUP BY department;

3. Window Functions

Perform a calculation across a set of rows related to the current row, without collapsing them into one row — RANK(), ROW_NUMBER(), LAG(), LEAD().

SELECT name, salary,
  RANK() OVER (ORDER BY salary DESC) AS salary_rank
FROM employees;

4. Table-Valued Functions

Return an entire table as their result, and can be queried just like a regular table.

CREATE FUNCTION dbo.GetEmployeesByDept(@dept VARCHAR(50))
RETURNS TABLE
AS
RETURN
  SELECT * FROM employees WHERE department = @dept;

💡 Tip: User-defined scalar functions can slow down large queries — prefer inline table-valued functions where possible for better performance.

Choosing the Right Function Type